Method of cooking sulphite pulp



G. H. TOMLINSON METHOD OF COOKING SULPHITE PULP Jan. 11, 1929. 1,697,032

Original Filed Dec. 7, 1925 INVENTOR GEORGEHTOMLINSON Patented slant l,T329 unrran starts l ddl ddt PATENT oversea GEORGE E. TOMLINSON, FMONTREAL QUEBEC; CANADA.

METHOD OF COOKING SULPHITE TULP.

Application filed December '2, 1925 Serial Nos73,860. Renewed may M,1923.

This invention relates to new and useful improvements in the method ofcooking sulphite pulp and the object of the invention is to provide asimple and efiicient method of a preparing the charge of pulp and themanner of cooking same,-so that the output from each charge will show adecided increase and a better grade of pulp, when compared with themethods at present in use.

Another object is to provide a method of cooking pulp in which thecharge will be cooked in a, more uniform manner and in a shorter spaceof time than in the methods of cooking usually employed.

A further object is to provide a'method of cooking sulphite pulp inwhich hot waste liquor from the blow pits will be used to increase thecapacity of the digester.

A still further object is to provide a method of cooking pulp, in whichthe hot fluid from the digester relief will be utilized to preheat thecooking acid.

Tn my invention, the wood chips are preheated and packed in a very closemanner within the digester, by utilizing the hot liqnor from the blowpit for doing same. When the digester is full of preheated chips, I thenintroduce preheated cooking acid and steam for the purposes of cookingthe chips.

In the drawings which are diagrammatic, I have shown devices of simpleconstruction which may be used in cooking sulphite pulp according to myinvention.

Figure 1 is a diagrammatic view of one form of apparatus which may beused for charging the digester.

Figure 2 is a diagrammatic illustration of a device for cooking thecharge.

Referring more particularly to the drawings, 11 designates a digesterand 12 the discharge end which is connected to a blow pit 13, by meansof the pipe 14 provided with a control valve 15. The blow pit isprovided with a drain cock 16 at its lower end which controls the flowof waste liquor to the trough 17. Also connected to the bottom of theblow pit is the inlet pipe 18 of the pump 19, the outlet from which isconnected to the top of a storage tank 20 by means of the pipe 21. Asuitable control valve 22 may be fitted in the connection between theblow pit and the inlet side of the pump, which may be driven from anysuitable source, such as the motor 23. Depending from the underside ofthe storage tank and communicating therewith is the discharge pipe 24,which may be provided with a suitable valve 25 for controlllng thepassage or flow of liquor therethrough. This pipe 24 may be made insectlons, so that it may be very easily dismantled when not required orduring the cooking of the charge in the digester. The end 26 of the p1pe24 is so positioned when in use that it communicates with the top of thedigester. Positioned above the digester is the chip storage bin27 whichcommunicates with the top of the digester by means of the chute 28 wh chmay be provided with a gate valve 29 to control the feed of chips to thedigester. The bottom of the digester is provided with a drain pipe 30,with a control valve 31 mounted therein. The top of the digester isprovided with a relief passageway or valve 32, in the cover of thedigester which with the cover may be removed to fill the digester. Thevalve 32 has an outlet pipe 33 which communicates with the bottom of thepressure tank 34, through the medium of the pipe 35. A valve 36 may befitted to the pipe 34 and in proximity to the junction between the pipes33 and 35. Cold cooking acid is stored in the tank 37, the outlet fromwhich is connected to a pump 38 driven by any suitable means such as themotor 39. The outlet from this pump 38 is connected to the pipe 35 bymeans of the pipe (10 which is provided with a valve 41. A pipeconnection 42 between the pipe 35 and the bottom of the digester may beprovided with suitable control valves 43 and at, one at each end thereonSteam from a suitable source (notshown) is fed, to the bottom of thedigester and to the pipe 35 through the medium of the main steam pipe 45and the branches 46 and 17 the former to the di'gester and the latter tothe pressure tank. A valve 48 may be mounted in the pipe 46 and valve 49may be mountedin the pipe 47. The

gauge pressure tank is provided with the glass 50 and a shut-ofi valve51 may be fitted in the pi e line 35 in close proximity to the bottom ofthe pressure tank. A'suitable drain valve 52 may also be fitted to thelower end of the pipe 35. A. relief valve 53 may be fitted to the top ofthe pressure tank.

The method of operation is as follows assuming that the digester isfilled with cooked sulphite. Valve 12 is opened and the charge withinthe digester blown by any suitable means into the blow pit 13. When thedigester is empty the cover is removed leaving the top of the digesteropen to receive a fresh charge of chips from the bin 27 Valve 18 isopened Gilli til) film

and pump 19 brought into operation to pump the hot liquor from the blowpit into the storage tank 20 from where it is led into the digesterthrough the pipe 24. Valves 25, 29 and 31 are then opened and valve 15closed. The wood chips and the hot liquor flow lnto the digester throughthe top opening, the liquor draining off through connection 30. In thisway, the hot liquor preheats the chips as they pass into the digesterand also washes them into position withinthe digester so that they arevery closely packed together. This method of packing the chips greatlyincreases the charge when compared with the methods at present in use inwhich the chips are fed and settled into position in the digester bygravity alone and this increase in digester capacity may be as high as15%, a considerable advantage and saving over the present feedingmethods. Also by using the hot liquor from the blow pit further savingis made in the cooking operation since the chips are raised intemperature to approximately thatof the liquor with which they come in Icontact. This heat in the past has been discharged as waste. To completethe cooking of the charge, valves and 29 are closed and the'cover isconnected to the top of the digester after all the feeding mechanism hasbeen removed therefrom. The liquor fed to the digester having drainedoff through the pipe 30, valve 31 is closed. It is now necessary tointroduce sulphite cooking acid and steam to complete the cooking. Nowif cold acid is introduced 0? fed into the digester, the heat which thechi as contain will be transferred to the acid as it diffuses throughthe mass and as a result of this the heat will be localized. Whetherthis localization of the heat occurs at the top or the bottom willdepend upon whether the acid is fed from the top or the bottom. Ineither case it is equally objectionable, since the wide differential intemperature thus occurring is ditficult to correct and makes for poorcooking conditions and may result in high screening losses.

In the operation of this method the cooking acid is heated before it isintroduced into the digester from the pressure tank 34. The cold acid ispumped from tank 37 into tank 34 through the-operation of pump 38 andthe manipulation of valves 41 and 51. Gas and steam which is relievedduring the cooking and finishing of the digester earlier in the seriesand in which this charge of acid may subsequently be used, is introducedto the pressure tank directly and without intermediate cooling throughthe operation of valves 32 and 36.

In this way perfect recovery of the excess sulphur dioxide gas is madeand at the same time the otherwise large amount of heat which iscustomarily abstracted by coolers is regenerated and thus used forheating the cooking acid. Steam may also be used to further heat theacid through manipulation of valve 49. By these means, the temperatureof the cooking acid may be raised toapproximately 100 C. beforeintroducing it into the digester. ..The digester havingbeen filled withpreheated chips in the manner previously described and the charge ofcooking acid having been prepared and preheated as described, thecooking acid is now admitted to the digester through manipulation of thevalves 44 and 43. The fact that both the cooking acid and chips havebeen preheated to approximately the same temperature, insures a more orless uniform initial temperature in the digester and thus obviates anydifliculty in bringing about the further heating or cooking operationswithin the digester. In this way it is possible to commence the cookingoperation with an initial temperature closely approximating 100 (3., inplace of 30 to 40 C. as under present methods. It will readily be seenthat by starting the cooking of the pulp at this high temperature, agreat saving in time can be made when compared with the older methods.Steam is introducedinto the digester through pipe 46 by manipulatingvalve 48, for the purpose of raising the temperature within I thedigester to the temperature at which it is desired to finish the charge.

Having thus described my invention, what I claim is 1. In a sulphitecooking process, themethod which consists of utilizing hot liquordischarged with the cooked pulp from a digester into a blow pit topreheat, and wash into position a second charge of chips in thedigester, and mixing with the second charge a quantityof cooking acidwhich has been raised in temperature, by the fluid passing'through therelief of the-digester while the first mentioned charge of pulp wasunder cooking conditions.

2. In a sulphite cooking process, the method which consists of utilizinghot liquor discharged with pulp which has been cooked in a digester topack, preheat and wash into position a second charge of pulp fed intothe digester, and mixing with said second charge a quantity of cookingacid which has been raised in temperature by means of steam and thegases passing from the relief of the digester during the cooking of thefirst mentioned charge of pulp.

3. In a sul'phiteco'oking process, the method which consist'sotutilizing the relief of gases from one charge of pulp to preheat coldcooking acid, discharging the pulp when cooked into a container andutilizing the hot liquor ofsaid discharge to preheat and wash intoposition a second charge of chips, draining off the liquor from thesecond charge of chips, raising the temperature of the cooking acid tothe temperature of the second charge of chips by steam, feeding the hotacid to women the second charge of chips and'then. cooking same byintroducing st.

4%. A process of cooking pulp which consists, in preheating a charge ofchips in a digester or container by means of hot liquor discharged withthe cooked pulp in a previous digesting operation, preheating a chargeof cooking acid in another container loy means of .hot gases alsoobtained from a previous digesting operation, bringing the two preheatedmaterials together by diffusing the hot acid through the hot chips, andthen. introducing steam. to complete the cooking operation.

5, A process of cooking sulphite pulp which consists, in preheating acharge of chips in a digester orcoutainer to a temperature ofapproximately 100 C. by means of a hot liquor discharged with the cookedpulp in a previous digesting operation, preheating a charge of cookingacid in another container to a temperature of approiriinat/eiy 100 t. bymeans of hot gases also obtained as the result of a previous digestingoperation, bringing the two preheated materials together in a cligesterin such a manner as to maintain approximately the same temperaturebetween the chips and cooking acid, and then introducing steam into themass to complete the cooking operation.

it. A. process of cooking sulphite puip which consists, in reheating acharge oi chips in a digester y the introduction of hot liquiddischarged with the pulp the course of a previous digesting operation,heating a charge of cooking acid in another container by ineans of hotgases obtained a product of the aforesaid previous operation, thenintroducing, the cooking acid into the digester approximately the sametemperature as the chips whereby the temperature of the preheated massWill be substantially uniform, and then raising the teniperattire oi themass by means of steam to coinpiete the cooking operation.

L 0 A process cooking pulp which cone sists in preheating a charge ofchips in a digester by introduction of hot liquor dis-i charged with thecooked pulp at the end of a previous digesting operation, then drainingthe liquor from the digester, then. introducing into the digester hotgases given 0% in the course of the aforesaid previous digestingoperation and then introducing steam into the digester to raise thetemperature of the mass sufficiently to complete the cooking operation.

in Witness whereof, I have hereunto set my hand.

enonon H. 'roiuson.

